Conventionally, a heating device for melting snow on a road, heating a floor surface or the like is constituted by embedding a heat generating body below the road surface or the floor surface. According to such a heating device, heat generated from the heat generating body reaches the surface via the nearest path, and accordingly, only right above the heat generating body is heated. As a result, effect of uniform heating of to-be heated object is difficult to achieve over an entire region thereof.
Further, in such a heating device, an electric heater having a PTC characteristic, that is, a self temperature and the latent heat accompanied by the phase transition is absorbed to thereby store heat, may be used. In such a latent heat absorbing type heat storing agent, it is particularly important to absorb the latent heat in a short period of time in achieving effective use thereof.
However, according to a conventional heating device, a vessel (for example, pipe) enclosed with a heat storing agent is placed on an electric heater in a planar shape, or in otherwise, a recess portion is installed on the surface of a vessel in a shape of a planar plate enclosed with a heat storing agent, while a heat generating body of an electric heat line or the like is arranged in the recess portion, so that heat is absorbed by the heat storing agent by conducting electricity to the heat generating body.
Therefore, Joule's heat generated from the heat generating body is absorbed by the heat generating agent after radiating heat to the surrounding (lowering of temperature and energy amount) and via heat resistance of the vessel per se and accordingly, an energy absorbing rate of the heat storing agent is significantly low and effective absorption of latent heat is difficult. Further, an energy absorbing efficiency of the heat storing agent is low and therefore, only a heat storing agent having a low melting temperature can be used and an amount of the heat storing agent (heat storing capacity) cannot be increased.
Hence, it is a second object of the present invention control function may be used as a heat generating body. The heat generating body having the PTC characteristic is featured in that the current resistance value is increased in response to rise of self temperature by electricity conduction and the current value is lowered and accordingly, the heat generating body is excellent in controllability, safety and economic performance since constant temperature can be maintained without being controlled from outside.
However, according to the above-described conventional structure, it has been difficult to effectively utilize the PTC characteristic. That is, temperature of a vicinity of the heat generating body is locally elevated by electricity conduction, the current value of the heat generating body is lowered and it is difficult to heat the surrounding swiftly and uniformly.
Hence, it is a first object of the present invention to provide a heating device which is easy to achieve effect of uniform heating of the to-be heated object over an entire region thereof and which can effectively utilize a heat generating body having the PTC characteristic.
Meanwhile, conventionally, according to such a heating device, a heat storing agent storing heat of a heat generating body may be used. In such a case, as a heat storing agent, a heat storing agent of a latent heat absorbing type in which the phase is changed between a solid phase and a liquid phase by a change in temperature to provide a heat storing type heat generating body capable of swiftly absorbing latent heat, using a heat storing agent having a high melting temperature, and providing high heat storing capacity by effectively utilizing energy generated from a heat generating element, so as to achieve high efficiency formation of energy absorption of the heat storing agent.
Further, until now, various snow melting and heating methods utilizing far infrared ray radiation energy have been proposed in the market and applied in an experimental scale.
For example, in asphalt paving, following methods and others are proposed. In one method, heat generating lines are laid on a base layer of a pavement, and subsequently, an asphalt-road-paving material admixed by the far infrared emissive material are laid as a surface layer. In another method, a far infrared emissive layer is formed on the surface of an asphalt surface layer, while heat conducted from et heat source of heat generating lines, hot water pipes or the like under the ground is converted into far infrared ray radiation energy, so as to melt snow on a road surface.
However, it is the current state that in any of these methods, significant merit is not achieved in comparison with a conventional snow melting or heating method in accordance with a heat conduction system. Further, the current state is brought into a situation in which there frequently causes an accident of disconnecting or destruction of the embedded heat source portion by impact load, vibration or the like from the surface of the surface layer. Further, in the case of embedding the heat source portion under the surface layer in such a way, there causes a problem in which interface cleavage is caused between the surface layer and the heat source portion by repeated elongation and contraction caused by impact, load and vibration from the surface of the surface layer or a variation in temperature in the road, which amounts to destruction of the surface layer such as crack or the like.
Hence, it is a third object of the present invention to provide a protective sheet for a heating device by which in a heating device, protection and strengthening of a total of device is achieved by achieving protection of a heat source portion and promotion of strength and durability of a surface layer of a road, a floor or the like and effective use of far infrared radiation energy can be achieved.